Why should I bother with unit testing if I can just use integration tests?

Question

Ok, I know I am going out on a limb making a statement like that, so my question is for everyone to convince me I am wrong. Take this scenario:

I have method A, which ca

Answer 1

Integration tests suffer from a form of combinatorial explosion: Say method A has 5 different ways to behave (different edge cases, etc.), and so has method B. If you test them together, there are now in theory 25 different cases you have to test! Yes, many of them may end up being the same, or can't occur for one reason or another, but basically, the more things you test together, the more impossible it becomes to test all edge cases.